ci: add GitHub Actions workflow for automated testing and linting

[RogueTex]

The project currently has no CI/CD pipeline to automatically validate code quality and run tests.

Adding a GitHub Actions workflow would:

• Automatically run tests on every push and pull request
• • Enforce code quality standards via linting
• • • Catch regressions and issues before they reach the main branch
• • • • Provide feedback to contributors
        The workflow should:

1. Trigger on push and pull request events to the main branch
2. 2. Set up Node.js environment (v18+)
3. 3. Install dependencies (npm install)
4. 4. Run linting checks (if linter is configured)
5. 5. Run any available tests (npm test or similar)
6. 6. Also support Python backend testing if configured